An Afghan security force member stands at the site of a car bomb attack in Kabul on May 31, 2017. (Photo credit should read SHAH MARAI/AFP/Getty Images)

A suicide attacker struck the fortified heart of the Afghan capital with a massive truck bomb Wednesday, killing 90 people, wounding 400 and raising new fears about the government's ability to protect its citizens nearly 16 years into a war with insurgents.

The bomber drove into Kabul's heavily guarded diplomatic quarter during the morning rush hour, leaving behind a bloody scene of chaos and destruction in one of the worst attacks since the drawdown of foreign forces from Afghanistan in 2014.

Most of the casualties were civilians, including women and children, said Ismail Kawasi, spokesman of the public health ministry. But the dead also included Afghan security guards at the facilities, including the U.S. Embassy, while 11 American contractors were wounded — none with life-threatening injuries, a U.S. State Department official said.

"I have been to many attacks, taken wounded people out of many blast sites, but I can say I have ever seen such a horrible attack as I saw this morning," ambulance driver Alef Ahmadzai told The Associated Press. "Everywhere was on fire and so many people were in critical condition."

There was no claim of responsibility for the attack, which came in the first week of the Muslim holy month of Ramadan. The Taliban flatly denied any involvement in an email to news outlets and condemned all attacks against civilians.

The explosives were hidden in a tanker truck used to clean out septic systems, said Najib Danish, deputy spokesman for the interior minister. The number of dead and wounded was provided by the Afghan government's media center, citing a statement from the Afghan Ulema Council, the country's top religious body that includes Muslim clerics, scholars and men of authority in religion and law.

The blast gouged a crater about 5 meters (15 feet) deep near Zanbaq Square in the Wazir Akbar Khan district, where foreign embassies are protected by a battery of their own security personnel as well as Afghan police and National Security Forces. The nearby German Embassy was heavily damaged.

Also in the area is Afghanistan's Foreign Ministry, the Presidential Palace and its intelligence and security headquarters, guarded by soldiers trained by the U.S. and its coalition partners.

"The terrorists, even in the holy month of Ramadan, the month of goodness, blessing and prayer, are not stopping the killing of our innocent people," said President Ashraf Ghani.

Afghanistan's war, the longest ever involving U.S. troops, has shown no sign of letting up, and the introduction into the battle of an Islamic State affiliate has made the country only more volatile.

Although they are small in number, militants from the Islamic State in Khorasan — an ancient name for parts of Afghanistan, Iran and Central Asia — have taken credit for several brazen assaults on the capital.

"Let's be clear: This is an intelligence failure, as has been the case with so many other attacks in Kabul and beyond. There was a clear failure to anticipate a major security threat in a highly secured area," said Michael Kugelman of the U.S.-based Wilson Center.

"The fact that these intelligence failures keep happening suggest that something isn't working at the top, and major and urgent changes are needed in security policy," he said by email.

Still, there are questions about whether a U.S. pledge to send more troops to Afghanistan will curb the violence.

"The sad reality is that more foreign troops would not necessarily ensure these attacks happen less," Kugelman said. "But they could help by supplementing training programs meant to enhance Afghan intel collection capacities, which have long been a deficiency in Afghanistan."

There are currently 8,500 U.S. troops in Afghanistan with a U.S. promise of more to come.

Afghan lawmaker and analyst Nasrullah Sadeqizada bemoaned the abysmal security, saying "the situation is deteriorating day by day."

In an interview, Sadeqizada criticized U.S. and NATO troops in Afghanistan, saying they have done little to improve protection in the country.

"If the situation continues to deteriorate, Afghans will lose all trust in the foreigners who are in Afghanistan as friends," he warned.

Gen. Mirza Mohammad Yarmand, former deputy interior minister, said more troops won't help, although he urged the global community to stay committed to Afghanistan.

"I don't think that more U.S. or NATO soldiers can solve the security problems in Afghanistan," he said.

"When we had more than 100,000 foreign soldiers, they were not even able to secure Helmand province" in southern Afghanistan, where the Taliban controls roughly 80 percent of the area, he said.

In the past year, U.S. troops have largely focused on thwarting a surge in Taliban attacks.

The stricken neighborhood was considered Kabul's safest, with the embassies protected by dozens of 10-foot-high blast walls and government offices guarded by security forces. More than 50 cars were either destroyed or damaged.

"I've never seen such a powerful explosion in my life," said Mohammad Haroon, who owns a nearby sporting goods store. All the windows in his shop and others around him were shattered, he added.

Shocked residents soaked in blood stumbled in the streets before being taken to hospitals. Passers-by helped them into private cars, while others went to the nearby Italian-run Emergency Hospital.

Besides the German Embassy, damage was reported at the embassies of China, Turkey, France, India and Japan, according to officials from those countries. Other nearby embassies include those of the U.S., Britain, Pakistan and Iran, as well as the NATO mission.

Nine Afghan guards at the U.S. Embassy were killed and 11 American contractors were wounded, with one Afghan guard missing, according to a U.S. State Department official, who was not authorized to talk publicly on the matter and spoke on condition of anonymity. None of the wounded Americans appeared to have life-threatening injuries, the official said.

The BBC said one of its drivers was killed and four of its journalists were wounded. Afghanistan's private TOLO Television also reported a staffer killed; Germany said an Afghan security guard outside its embassy was among the dead.

German Foreign Minister Sigmar Gabriel said that along with an Afghan guard who was killed, a German diplomat was slightly wounded and an Afghan staffer had severe injuries.

Chancellor Angela Merkel condemned the attack, saying that "terrorism has no borders."

It "targets all of us — whether in Manchester or Berlin, Paris, Istanbul, St. Petersburg or today in Kabul," she said in the southern German city of Nuremberg.

"Today we're united in shock and sadness across all borders," she added.

She vowed: "We will lead the fight against terrorism, and we will win it."

Germany has had troops in Afghanistan for 15 years, primarily in the north in and around Mazar-e-Sharif. It is one of the biggest contributors to the NATO-led Resolute Support mission, with about 980 soldiers supporting and training Afghan forces.

Neighboring Pakistan's Ministry of Foreign Affairs said the bomb damaged residences of some of its diplomats and staff and caused some minor injuries.